Oceanic variability associated with the Madden-Julian oscillation
This study investigates the basin-wide oceanic variability associated with the Madden-Julian Oscillation (MJO) using new observations from the global array of profiling floats, known as Argo. Analysis of the Argo gridded data in a case study of the December 2003 to February 2004 MJO event in the Pacific Ocean reveals that the oceanic variability along the equator is characterised by an eastward propagating Kelvin wave response to the MJO surface wind stress anomalies. The observed phase speed and latitudinal structure are characteristics of the first baroclinic mode Kelvin wave. The vertical structures of these Kelvin waves are observed for the first time to extend downward to 1500 m. The amplitude of the deep ocean temperature anomalies is up to three times the amplitude ofthe observed annual cycle. With unprecedented coverage of salinity observations in the deep ocean provided by the Argo data, systematic changes in subsurface salinity variability during the MJO event are revealed for the first time. It is found that the salinity changes are associated with the Kelvin wave displacing isopycnals vertically. The composite study for the full period of the data set from January 2003 to December 2006 confirms the dominance of the Kelvin wave response in the subsurface temperature and salinity variability in the Pacific Ocean. Composites of sea surface temperature and sea surface salinity anomalies suggest the role of horizontal advection mediated by the Kelvin waves in addition to the MJO associated surface heat and fresh water fluxes variation. In the Indian Ocean, there is some evidence of a dynamical response to surface wind stress changes in the form of local upwelling and downwelling along 0°_5° Sin the central basin as well as in the equatorial eastern basin. However, the response did not exhibit propagating characteristics similar to the Pacific Ocean counterpart.